1. Field of the Invention
This invention, in general, relates to artificial lighting devices and, in particular, to a reflector for use with a light source to project a beam of illumination having a substantially constant intensity over a predetermined solid angle.
2. Description of the Prior Art
The utilization of reflectors to intercept radiation emanating from a source and redirect such radiation in a controllable manner for the purpose of making more efficient use of the source radiant energy and of achieving preferred distributions in the intensity of illumination falling on a subject from the reflector-source combination is a well-established practice in the optical arts.
Reflector shape is extremely important in determining how much of the source radiation is usefully concentrated on a subject. Spherical reflectors, for example, produce broad spreading beams for general illumination of a subject and have been used for flash and photoflash lamps used as flash or fill-in lights.
Parabolic reflectors, on the other hand, are used mostly to give a fairly parallel beam for illuminating only a part of a subject or for illuminating the whole of a distant object.
Elliptical reflectors provide convergent beams when a source is placed at one of the reflector focal points--the light converges to the other focus. This type of reflector is particularly suitable for use in illuminating relatively small areas such as the negative in an enlarger or projector.
Aside from reflector shape, other factors, such as reflector size and source geometry and placement within the reflector, also influence the performance of lighting devices. In general, large reflectors placed close to a source make more efficient lighting devices than those using smaller reflectors spaced farther from a source. In addition to being less efficient, small curved reflectors having short focal lengths, used in combination with point sources, do not generally provide uniform illumination. This is a serious disadvantage particularly where the size of a lighing device is important and, also, because most practical sources have some finite size and therefore cannot be regarded as point sources. Consequently, as reflector focal length is reduced, the effect of the size of a light source becomes more and more pronounced.
Where uniform lighting is desirable and size is a limitation, it has been the practice to use a light source as compact as possible in conjunction with the largest convenient reflector whose shape has been carefully selected, usually experimentally, to control light so that the intensity of illumination is distributed as uniformly as possible. In addition, it is also known for this purpose to utilize auxiliary optics such as Fresnel lenses and refracting plates to achieve uniformity.
It is a primary object of the present invention to provide a compact artificial lighting device for uniformly illuminating a subject.
Another object of the present invention is to provide a reflector whose shape, when used in conjunction with a point source or an approximate point source, provides a substantially even illumination intensity over a predetermined solid angle.
Yet another object of the present invention is to provide an elongated reflector which, when used with an elongated cylindrical source, provides an illumination distribution whose intensity is substantially constant along at least one line in a plane normal to the general direction along which light is projected from the reflector.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.